The invention relates to a new way of combining a certain number of elementary amplifiers, constituted more particularly by field effect transistors formed on the same semiconductor wafer with a view to obtaining a monolithic amplifier having a high power on a wide pass band, all the means used being integrated on the same semiconductor wafer.
The power of a field effect transistor is directly proportional to the width of the gate all other things being equal. The only widely used solution at present for obtaining a significant power without introducing losses which may reduce the gain, consists of the connection in parallel of a certain number of identical transistors, whose width is typically 100 to 200 .mu.m. The obtainable power levels are approximately 0.5 W/mm of gate (1 W/mm in the laboratory) in the X band. Thus, the number of elements to be connected in parallel is approximately 10 to 20 per watt. The longitudinal size of each transistor is dependent on the way in which the source is connected to earth and is typically 50 to 150 .mu.m for transistors in the X and Ku band. Thus, on average a longitudinal size of approximately 0.5 to 1 mm/W is obtained by connecting in parallel.
However, all the metallic connections produced for performing the connection between these elements (gates and drains) form, with the metal base to which the amplifier is welded, a propagation line whose wavelength is approximately 10 mm to 10 GHz (on gallium arsenide). Thus, as from a power of a few watts the dimensions of the connections become approximately a quarter of the wavelength. As from then the uniformity of the power distribution between the different elements becomes impossible and the performance levels can no longer be proportional to the number of elements. For this reason amplifiers are produced in the form of "modules", whose power generally does not exceed 1 watt in the X band.
Several modules must be connected in parallel to obtain amplifiers of a few watts. It is known to carry out this connection in parallel by using dividers-recombiners produced on supports different from those of the modules. Quite apart from the technological difficulties this method does not give good results if the modules are not strictly identical and are not placed on paths of strictly identical length.
A partial solution to these problems is provided by using a WILKINSON phase splitter comprising ballast resistors. A star arrangement involving a distribution over a cylinder of transistors and their matching elements makes it possible to obtain a high power level, but has the disadvantages of an amplification band of a very limited width and a very complex construction.
The use of so-called LANGE couplers makes it possible to obtain a pyramidal cascade of couplers (in pairs) as a result of which a wide frequency band is obtained. However, the combination of a large number of elementary amplifiers leads to considerable complexity.
The patent application filed by the Assignee Company in the United States under Ser. No. 218,101 on Dec. 19, 1980, in Japan under No. 00 3697/81 on Jan. 13, 1981 and in France on Jan. 15, 1980 under NO. 80 00 845 describes a high frequency power distributor using a travelling wave divider. In an amplifier equipped with such a system the power is progressively distributed over the different amplifier modules as a function of the propagation along an input divider. Putting back into phase is brought about by using a structure of the same type for the recombination of the powers at the output. Resistors deposited on the semiconductor plates of the modules ensure both the balancing between the channels and the absorption of the reflected waves due to the mismatches of the modules.